This invention relates to the manufacture of interconnecting conductors or conducting bodies and relates to a method for the simple, inexpensive manufacture of extremely thin and extremely finely structured, shielded or screened interconnecting conductors.
Modern electronics are developing at a very rapid pace and require ever more inexpensive and ever more compact components. Reference is made as an example to printed circuit boards, which have ever higher interconnection densities and carry and connect ever more electronic components such as Surface Mounted Devices (SMD) or Leadless Ceramic Chip Carriers (LCCC). Particular reference is made to the substrates for the production of Multichip Modules (MCM), which increasingly carry and connect uncased components (bare Si-chips).
Such an increase in the interconnection density of printed circuit boards is implemented in accordance with the DYCOstrate(copyright) method and is, e.g., disclosed in published international application WO93/26,143. Thin plastic films are plasma- or chemically-etched for forming electric plated-through holes and for electrical passages in the z-direction. This method allows simultaneous, very expensive production of very small holes with a selectable shape. Beside a massive increase in the attainable interconnection density, the DYCOstrate(copyright) process has a number of further advantages, which are described in the aforementioned document.
The high interconnection density in the case of non-uniform conductor spacing of modern printed circuit boards leads, in high frequency applications (frequency greater than 1 GHz) to problems, such as excessive attenuation and undesired reflections or cross-talk of signals. Therefore, the interconnecting conductors of the printed circuit boards must have a very uniform mutual spacing or, even better, they must be produced as partly or completely shielded interconnecting conductors.
An object of the present invention is to provide a method for bringing about simple, inexpensive manufacture of electrically screened or shielded interconnecting conductors from etchable semifinished foil products with extremely thin and extremely fine conductor configurations. Use is made of known, proven procedures, materials, etc. For example, the known wet chemical process is used for producing the conductor configurations or structures. These interconnecting conductors must be compatible with known systems, such as the DYCOstrates(copyright) process with regards to the further processing and, in particular, assembly and application. In addition, the manufacture of the interconnecting conductors using semifinished foil products must be suitable for use automatically, e.g. roll-to-roll, and in a batch operation by charging, e.g., the use of support plates must also be possible.
It has surprisingly been found that in the DYCOstrate(copyright) process not only point-like arranged, electric vias or through-holes in the z-direction but also surface vias in the z-direction (openings in the form of slots or grooves) can be precisely produced. This is utilized according to the invention in order to shield the signal conductors in a specific layer of a semifinished foil product by producing surface vias of shielding material in other layers. These shielding material vias are obtained by winding the shielding material around the signal conductor insulated by dielectric material. This winding around can take place by plating-on (electrodeposition) further shielding material, or by screen printing, dispenser application and manual application of further shielding material. Thus, one or more signal conductor layers can be partly or completely shielded. This production of shielded interconnecting conductors from, e.g., etchable semifinished foil products with extremely thin and extremely fine conductor configurations is compatible with standard procedures of the printed circuit board industry and with the DYCOstrate(copyright) process.
A first semifinished foil product with at least one layer of conductors comprising signal conductors and shielding conductors is connected with at least one further semifinished foil product with shielding material. Advantageously, the shielding material is laminated on by dielectric material with at least one layer of conductors. In a photochemical structuring, the shielding material is provided with openings extending to the dielectric. In a chemical or plasma etching process, or also using laser ablation, the dielectric is removed in accordance with said openings extending to the shielding conductors. The edges of the openings in the shielding material are electrically contacted with said shielding conductors, so that shielding is provided by dielectric-insulated signal conductors, as well as shielding conductors and shielding material.